Income Taxes - Deferred Income Tax Assets (Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Deferred income tax assets:
Accrued liabilities	$ 54,906	$ 54,971
Retirement plans and postretirement benefits	12,190	10,379
Share-based compensation	2,343	3,886
Receivables and inventories	6,789	6,651
Derivative financial instruments	1,075	99
Net operating loss carryforwards	61,009	38,023
Tax credits and other carryforwards	23,195	9,965
Valuation allowances	(40,966)	(21,755)
Deferred income tax assets	120,541	102,219
Deferred income tax liabilities:
Property, plant and equipment	(113,272)	(124,185)
Intangible assets	(14,475)	(22,213)
Cancellation of debt	0	(1,708)
Other	(3,983)	(3,400)
Deferred income tax liabilities	(131,730)	(151,506)
Net deferred income tax asset (liability)	(11,189)	(49,287)
Deferred tax assets related to uncertain tax positions	$ 5,400	$ 7,000